What is a Foil Resistor? The metal foil resistor has the best precision and stability properties of all resistor types. The foil is made of an alloy of usually Nichrome with additives. It is mounted on a ceramic carrier with high heat conductivity. The foil has a thickness of only several micrometers. The desired resistance value is achieved by a photoetched resistive pattern in the foil. The metal foil resistor has a low Temperature Coefficient of Resistance (TCR), good long term stability, low noise, low capacitance, fast thermal stabilization and no inductance. The low TCR is one of the most important parameters that influence the stability. This means that the resistance value will vary only a small amount as the ambient temperature and the resistor’s internal temperature changes. Over a range from 0 till 60 deg C, a typical value for TCR is around 1 ppm per deg C. This depends on the construction (thermo-mechanical effects) and the properties of the foil material. In the planar foil the pattern is made parallel to reduce inductance (max 0.08 microH). Foil Resistor Definition A foil resistor is a high precision component to limit electric current. The opposition to current flow is provided by a very thin piece of metal. Metal Foil Resistor Characteristics The excellent properties for precision and stability are due to a combination of several characteristics, which are following from the design principles of the metal foil resistor. Temperature Coefficient, Resistance (TCR) – Foil resistors achieve a low TCR by taking advantage of two characteristics of the foil. The resistance of the foil naturally increases as temperature increases. The resistor is manufactured so that rising temperature causes compression of the foil. This makes the resistance drop as temperature rises. The total effect is one of very little resistance change as...
[Read more]
Tag: